By Matthew A. Ward

PORTSMOUTH, Virginia (Reuters) - A man who admitted to strangling two fellow prison inmates and threatened to continue killing until he received the death penalty was executed in Virginia on Wednesday, the first time the state has used the electric chair in nearly three years.

Robert Charles Gleason Jr., 42, had said he wanted to be put to death despite attempts by his former court-appointed attorneys to halt the execution and have him undergo a mental competency evaluation.

The attorneys had argued the time he spent in solitary confinement on death row left him unable to make rational decisions, a claim authorities rejected.

Gleason was pronounced dead at 9:08 p.m. (0208 GMT on Thursday), said Larry Traylor, a spokesman for the Virginia Department of Corrections. In his last statement, Gleason uttered the Irish Gaelic phrase "Pog mo thoin," or "Kiss my ass," Traylor said.

Gleason was the first inmate in the United States to be executed this year, according to the Death Penalty Information Center, a group that tracks capital punishment cases.

Virginia is one of nine U.S. states where inmates can choose to be executed either by electrocution or lethal injection, the more commonly used method to carry out executions in the United States.

Gleason was serving life in prison without parole for a 2007 murder when he admitted to using strips from bed sheets to bind and strangle Harvey Watson, a 63-year-old inmate at Virginia's Wallens Ridge State Prison in May 2009.

According to court documents, Gleason told authorities he timed the murder to coincide with the second anniversary of the previous homicide he carried out.

He admitted to tying Watson's hands without a struggle after telling him he had come up with a way for the two to escape. Court records show he taunted Watson before he strangled him by pressing a urine-soaked sponge onto his face and a sock into his mouth.

Gleason attacked another inmate in July 2010 at the maximum-security Red Onion State Prison while he waited to be sentenced for killing Watson, according to court records.

Gleason said he asked fellow inmate Aaron A. Cooper, 26, to try on a "religious necklace," which Gleason threaded through a wire fence separating the two while they were in solitary recreation pens. Continued...